1. Field of the Invention
The present invention relates to a motor such as a spindle motor that drives a magnetic disk for a hard disk drive used in a computer, and a method of manufacturing the same.
2. Description of Related Art
Recently the capacity of the hard disk drive has been increasing. Accordingly the hard disk drive requires employment of a motor capable of rotating at higher speeds so as to cope with the capacity increase. Instead of a ball bearing that has been generally employed for the motor, a fluid bearing has been increasingly applied to satisfy the requirement of the motor rotating at higher speeds.
There is one known motor using a fluid bearing in a hard disk drive, an example of which is shown in FIG. 5. In FIG. 5, a motor 1 (a spindle motor for driving a magnetic disk) includes a stator 3 disposed on a flange 2 and a rotor 4 having a magnet 5 opposing the stator 3.
The flange 2 is generally formed of a flange body 6 for holding the stator 3, and a sleeve 7 press fitted into a hole (sleeve fitting hole 6a) formed in the flange body 6.
The sleeve 7 is generally composed of a cylindrical sleeve body 9 having an annular stepped portion 8 formed in the inner diameter portion at one end, an annular member 10 fitted in the annular stepped portion 8, and a disc-like counterplate 11. The counterplate 11 and the sleeve body 9 are air-tightly bonded by, for example, welding.
A shaft 12 of the rotor 4 is inserted into a hole (as a sleeve hole 7a) formed inside of the sleeve 7 (the sleeve body 9 and the annular member 10). A fluid bearing 13 is defined by the shaft 12 and the sleeve 7. An oil 14 is used as the fluid for the fluid bearing 13 in this example. It is, however, clearly understood that the oil may be replaced by gas such as air.
A plurality of grooves 15 are formed on the inner peripheral wall (sleeve hole 7a) of the sleeve body 9. A plurality of grooves (not shown) are also formed on the end portion of the annular member 10 in contact with the stepped surface of the sleeve body 9, and on the portion of the counterplate 11 in contact with the annular member 10. The space between the sleeve 7 and the shaft 12 including the grooves 15 and other grooves (not shown) are sealed with the oil fluid 14.
The oil fluid is compelled to form an oil film between the sleeve 7 and the shaft 12 under a dynamic pressure generated by a pumping effect of the rotating shaft 12. The shaft 12, thus, is allowed to rotate relative to the sleeve 7 through the oil film.
The sleeve body 9 is press fitted with the hole (sleeve fitting hole 6a) of the flange body 6 before mounting the stator 3 onto the flange body 6. In the state where the flange body 6 and the sleeve body 9 are assembled, the sleeve hole 7a (or the inner peripheral wall of the sleeve 7) is machined. The stator 3 is mounted onto the flange body 6, and then the annular member 10 and the counterplate 11 are assembled to the sleeve body 9 to constitute the sleeve 7. The shaft 12 of the rotor 4 is inserted into the sleeve hole 7a of the resultant assemble body of the sleeve 7 and the flange body 6. During the insertion of the shaft 12, the oil fluid 14 is poured into the vacuum space between the shaft 12 and the sleeve 7. The sleeve body 9 and the counterplate 11 are air tightly bonded by, for example, welding at the outer peripheral contact portion. Under the vacuum state of the space between the sleeve 7 and the shaft 12, the differential pressure with respect to the outside (atmospheric pressure) acts on the oil fluid 14 so as to prevent leakage thereof.
When press fitting the sleeve body 9 into the hole (sleeve fitting hole 6a) of the flange body 6, the pressure generated by the press fitting of the sleeve body 9 deforms the sleeve hole 7a (inner peripheral wall). The deformation may cause assembly failure that cannot allow the uniform clearance to be kept between the sleeve hole 7a and the shaft 12. Therefore the sleeve hole 7a (inner peripheral wall) is machined after press fitting the sleeve body 9 into the flange body 6 so as to cope with the deformation. The shaft 12, then, is inserted into the sleeve hole 7a to define the fluid bearing 13.
In case of the aforementioned motor 1, the sleeve hole 7a (inner peripheral wall) is machined in the state where the flange body 6 and the sleeve body 9 are assembled together. As the sleeve hole 7a has to be machined in a large assembled unit of the flange body 6 and the sleeve body 9, a large-sized jig that matches at the process of the large assembled unit is required. Since the assembled unit has a large size and a complicated configuration, the work efficiency is deteriorated, working time is elongated owing to the use of the large jig, and assembling work is complicated that may hinder automatization. In addition to the deteriorated productivity, the cutting fluid or the like tends to infiltrate into the press fitting point because the machining process is conducted after the press fitting. It is, therefore, difficult to completely remove the infiltrated cutting fluid even by cleaning. Therefore, the residual stained water may cause generation of outgas during actual operation.
The present invention has been made in consideration of the foregoing problem. It is, therefore, an object of the invention to provide a motor and a method of manufacturing the motor, which may prevent deformation of the sleeve hole (inner peripheral wall) due to the force generated by press fitting of the sleeve and may facilitate assembling work, thus improving the productivity and eliminating the cause of outgas.
According to a first aspect of the present invention, there is provided with a motor in which a rotor is provided with a magnet opposing to the stator of the flange that includes a flange formed of a flange body for holding a stator and a sleeve which is shrinkage fitted (or lightly press fit bonded) into a hole formed in the flange body, receives a shaft of a rotor inserted through an inner hole, and defines a fluid bearing together with the shaft, wherein a recess is formed at an opening of a wall with a hole of the flange body to relieve a press fitting force exerted to the sleeve.
According to a second aspect of the present invention in the first aspect, the recess is of an annular shape.
According to a third aspect of the present invention in the first aspect, the recess constitutes a grooved portion formed at an opening of the hole formed on the wall and/or a grooved recess formed on the inside area of the hole formed on the wall.
According to a fourth aspect of the present invention in the third aspect, the recess and/or a recess portion is of an annular shape.
According to a fifth aspect of the present invention in the motor of any one of the first to the forth aspects, wherein the sleeve is provided with a substantially cylindrical flange body into which the shaft is inserted, and a portion corresponding to the flange body and a portion corresponding to the sleeve body are integrally formed.
According to a six aspect of the present invention, there is provided with a motor that includes a flange formed of a sleeve having a lower bulge and a flange body, wherein a rotor is provided with a magnet opposing to a stator of the flange, and the stator is supported by the lower bulge of the sleeve.
According to a seventh aspect of the present invention, there is provided with a method of manufacturing a motor in which a rotor is provided with a magnet opposing to the stator of the flange, including a flange formed of a flange body for holding a stator and a sleeve which is provided with a recess and press fitted into a hole formed in the flange body, receives a shaft of a rotor inserted through an inner hole, defines a fluid bearing together with the shaft, and is further provided with a flange body having a substantially cylindrical shape into which the shaft is inserted, which includes the steps of press fitting the sleeve body finished by machining into a hole of the flange body, and inserting the shaft of the rotor into the hole of the sleeve body so as to define a fluid bearing.
In this case, the finished sleeve body is press fitted into the hole of the flange body. The subsequent process conducted to clean up the infiltrated cutting fluid is omitted.
According to an eighth aspect of the present invention in the seventh aspect, the recess is of an annular shape.
According to a ninth aspect of the present invention in the seventh aspect, the recess constitutes a cut off portion formed at an opening of the hole formed on the wall and/or a grooved recess formed on the inside area of the hole formed on the wall.
According to a tenth aspect of the present invention in the ninth aspect, the recess and/or a recess portion is of an annular shape.
According to an eleventh aspect of the present invention, there is provided with a method of manufacturing a motor including a flange formed of a sleeve having a lower bulge and a flange body, wherein a rotor is provided with a magnet opposing to a stator of the flange, and the stator is supported by the lower bulge of the sleeve, which includes the steps of press fitting the lower bulge of the sleeve body finished by machining into a hole of the flange body, and inserting the shaft of the assembled rotor into the hole of the sleeve body so as to define a fluid bearing.